The panel itself is very easy since it has only a few mounting holes and cutouts for the controls. It is a bit more work to reproduce the image with all the machine settings and import it as vector graphic (plt format) into Front Panel Designer.
You can prepare the vector file with any graphic software.
Let me know if you need any help with this.

You don't need to specify the holes on Housing Profile 2. This is where you want to use our square nuts (GGSO9903). They slide right into Housing Profile 2. You can move them to the desired position and line them up with the cover panel.

You are right, there is no equation for placing a bracket on the slotted side of Housing Profile 2.
The distances for placing the bracket holes depend on your material thickness and if you keep the 2mm recommended remaining material to cover the slot. I can double check your design if you like, just email me your fpd files.

20kg is quite some weight. Remember the top panel is only supported on the sides and some housing brackets on front and back. Does your design allow a block within the enclosure for additional support?